US 20050243791 A1 Abstract A channel estimation apparatus and method for an OFDM/OFDAM receiver. A channel characteristic value, positioned prior to a pilot symbol of a current slot, from among data symbols of the current slot is estimated by a time-domain interpolation method for use with a channel characteristic value of a pilot symbol of a previous slot and a channel characteristic value of the pilot symbol of the current slot. A channel characteristic value next to the pilot symbol of the current slot from among the data symbols of the current slot is estimated by a time-domain extrapolation method for use with the channel characteristic value of the pilot symbol of the previous slot and the channel characteristic value of the pilot symbol of the current slot.
Claims(6) 1. A method for performing channel estimation using a pilot symbol positioned among data symbols of each slot in a time domain in a receiver for receiving an OFDM (Orthogonal Frequency Division Multiplexing) signal, comprising the steps of:
estimating a channel characteristic value associated with a data symbol, which is positioned prior to a pilot symbol of a current slot, from among data symbols of the current slot according to a time-domain interpolation method for use with a channel characteristic value of a pilot symbol of a previous slot and a channel characteristic value of a pilot symbol of the current slot; and estimating a channel characteristic value associated with a data symbol, which is next to the pilot symbol of the current slot, from among the data symbols of the current slot according to a time-domain extrapolation method for use with the channel characteristic value of the pilot symbol of the previous slot and the channel characteristic value of the pilot symbol of the current slot. 2. The method according to H
_{k,i}
=a
_{i}
×P
_{k−1}
+b
_{i}
×P
_{k }
where i is an index of an order number of data symbols contained in one slot, a
_{i }is a weight factor, which is applied to the channel characteristic value of the pilot symbol of the previous slot according to positions of individual data symbols contained in one slot, b_{i }is a weight factor, which is applied to the channel characteristic value of the pilot symbol of the current slot according to positions of individual data symbols contained in one slot, P_{k−1 }is a channel characteristic value of the pilot symbol of the previous slot, P_{k }is a channel characteristic value of the pilot symbol of the current slot, and H_{k,i }is a channel characteristic value estimated for an i-th data symbol from among the data symbols included in a slot. 3. The method according to _{i }is determined to be hd 1=½, a_{2}=¼, a_{3}=−¼, and the other weight factor b_{i }is determined to be 1−a_{i}, when the slot includes two data symbols, one pilot symbol, and one data symbol, which are sequentially connected in the time domain. 4. A channel estimator for performing channel estimation using a pilot symbol positioned among data symbols of each slot in a time domain in a receiver for receiving an OFDM (Orthogonal Frequency Division Multiplexing) signal, comprising:
a pilot reader for recognizing a current slot number using a data symbol number that identifies an order number of a data symbol to be channel-estimated from among data symbols contained in a single frame, and reading a channel characteristic value of a pilot symbol of a previous slot and a channel characteristic value of a pilot symbol of a current slot from an FFT (Fast Fourier Transform) unit on the basis of the recognized current slot number; and a channel estimation processor for estimating a channel characteristic value associated with a data symbol, which is positioned prior to the pilot symbol of the current slot, from among data symbols of the current slot according to a time-domain interpolation method for use with the channel characteristic value of the pilot symbol of the previous slot and the channel characteristic value of the pilot symbol of the current slot, and estimating a channel characteristic value associated with a data symbol, which is next to the pilot symbol of the current slot, from among the data symbols of the current slot according to a time-domain extrapolation method for use with the channel characteristic value of the pilot symbol of the previous slot and the channel characteristic value of the pilot symbol of the current slot. 5. The channel estimator according to a weight factor provider for storing weight factor pairs, each of which is includes first and second weight factors, which are respectively applied to the channel characteristic value of the pilot symbol of the previous slot and the channel characteristic value of the pilot symbol of the current slot according to locations of individual data symbols in one slot, and generating a pair of the first and second weight factors corresponding to the data symbol number; and a channel characteristic value generator for performing one of an interpolation method and an extrapolation method according to H _{k,i} =a _{i} ×P _{k−1} +b _{i} ×P _{k } upon receiving the channel characteristic value of the pilot symbol of the previous slot, the channel characteristic value of the pilot symbol of the current slot, and the first and second weight factors, and generating a channel characteristic value associated with the data symbol, where i is an index of an order number of data symbols contained in one slot, a _{i }is indicative of a first weight factor, b_{i }is a second weight factor, P_{k−1 }is the channel characteristic value of the pilot symbol of the previous slot, P_{k }is the channel characteristic value of the pilot symbol of the current slot, and H_{k,i }is a channel characteristic value estimated for an i-th data symbol from among data symbols included in a slot. 6. The channel estimator according to _{i }is determined to be a_{1}=½, a_{2}=¼, a_{3}=−¼, and the second weight factor b_{i }is determined to be 1−a_{i}, when the slot includes two data symbols, one pilot symbol, and one data symbol, which are sequentially connected in the time domain.Description This application claims priority to an application entitled “CHANNEL ESTIMATION METHOD FOR OFDM/OFDMA RECEIVER AND CHANNEL ESTIMATOR FOR THE SAME”, filed in the Korean Intellectual Property Office on Apr. 30, 2004 and assigned Ser. No. 2004-30567, the contents of which are hereby incorporated by reference. 1. Field of the Invention The present invention relates generally to an OFDM/OFDMA (Orthogonal Frequency Division Multiplexing/Orthogonal Frequency Division Multiple Access) transmission system, and more particularly to a method and apparatus for performing channel estimation using a pilot symbol in an OFDM/OFDMA receiver, such that channel distortion in the OFDM/OFDMA receiver can be compensated. 2. Description of the Related Art An OFDM scheme or an OFDMA scheme based on the OFDM scheme is a multi-carrier modulation scheme for the parallel-transmission of data using several sub-carriers having orthogonality therebetween, instead of using a broadband single carrier. The OFDM or the OFDMA scheme is based on the fact that individual narrowband sub-channels have flat fading characteristics even in a frequency selective fading channel with a very large ISI (Inter-Symbol Interference). The OFDM scheme determines its symbol in a frequency domain, such that an equalizer for the frequency domain is required to compensate for channel distortion associated with a received symbol. A transmission end of the OFDM transmission system transmits a data symbol and also transmits a pilot symbol used for channel estimation to equalize the data symbol. Technologies for selecting a pilot signal, which effectively estimates an OFDM channel and maintains a high transfer rate, and also a variety of OFDM channel estimation methods have recently been proposed. For example, a method for acquiring a channel characteristic value by averaging samples of the pilot signal in a time domain, and a method for estimating channel characteristics in a frequency domain using a mean squared error of the pilot signal and applying the estimated result to a signal compensation process have recently been introduced. Referring to The channel estimation in the channel estimator An exemplary pilot symbol for use in the OFDM scheme is illustrated in For the distribution format of the data and pilot symbols in the time domain, data is composed in slot units rather than symbol units, as can be seen from When one slot is configured as illustrated in Referring to Equations (1)-(3), assuming that a current slot with information to be recovered is determined to be a k-th slot, H Referring to Equations (1)-(3) and Referring to As can be seen from If channel estimation is carried out by using a first slot (i.e., Slot The channel estimation for the first data symbol of the OFDM frame of Referring to Equation (7), H Equation (7) is acquired from Equation (8) in the same manner as in Equations (1)-(3).
In order to recover any slot information using the aforementioned channel estimation method, a channel characteristic value of a current slot to be recovered, a channel characteristic value of a previous slot, and a channel characteristic value of the next slot must be used. Consequently, a buffer capable of temporarily storing channel characteristic values of pilot symbols of three slots including the current slot is required. Further, a delay is created during the channel estimation. Accordingly, the present invention has been designed in view of the above and other problems, and it is an object of the present invention to provide a channel estimation method and apparatus for reducing a size of a buffer required for channel estimation and reducing a delay. In accordance with the present invention, the above and other objects can be accomplished by a channel estimation method for estimating a channel characteristic value, positioned prior to a pilot symbol of a current slot, from among data symbols of the current slot according to a time-domain interpolation method for use with a channel characteristic value of a pilot symbol of a previous slot and a channel characteristic value of the pilot symbol of the current slot; and estimating a channel characteristic value next to the pilot symbol of the current slot from among the data symbols of the current slot according to a time-domain extrapolation method for use with the channel characteristic value of the pilot symbol of the previous slot and the channel characteristic value of the pilot symbol of the current slot. The above and other objects, features, and advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: Preferred embodiments of the present invention will be described in detail herein below with reference to the annexed drawings. In the following description, a detailed description of known functions and configurations incorporated herein will be omitted when it may obscure the subject matter of the present invention. Although Equations (9)-(10) are equal to Equations (1)-(2), respectively, Equation (11) is different from Equation (3). Therefore, it can be understood that H More specifically, the method of As can be seen from A data symbol not included in slots, i.e., a first data symbol (also called a header data symbol) of the frame of Referring to The slot selector The address counter The channel estimation processor In Equation (13), i is an index of the order of data symbols contained in one slot, a As described above, the present invention has been used in a case in which one slot includes two data symbols, one pilot symbol, and one data symbol connected in the time domain. However, provided that channel estimation is performed using a pilot symbol positioned between data symbols in a single slot even though the number of data symbols contained in the single slot or the location of the pilot symbol contained in the single slot is changed to another value, the present invention can also be used. Equation (13) is obtained by generalizing Equations (9)-(11) in consideration of the above case in which the number of data symbols in the single slot or the location of the pilot symbol in the single slot is changed to another value. Therefore, the weight factors a In
If the number of data symbols in one slot or the location of the pilot symbol in one slot is different from that illustrated in The weight factors a The symbol index selector The channel characteristic value generator Steps The channel characteristic value H Steps If the index i is equal to ‘3’ at step At step At step Accordingly, the channel characteristic values H As described above, the present invention estimates channel characteristic values using an interpolation or extrapolation for use with pilot symbols of only two slots, such that it minimizes performance deterioration caused by channel estimation, and at the same time reduces a buffer size consumed for channel estimation, and also delay. As can be seen from Particularly, although the present invention has been described above with reference to a specific case in which one slot includes two data symbols, one pilot symbol, and one data symbol, which are sequentially connected in a time domain as illustrated in Although preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions, and substitutions are possible, without departing from the scope and spirit of the present invention as disclosed in the accompanying claims. Referenced by
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